Countries around the world have introduced specific limits relating to climate parameters in cages for experimental animals. Typically, it is specified that the animals must be kept in air with relatively narrow tolerances on temperature, relative humidity etc. In the following description, the wording “climate parameters” covers those variables which may influence the climate and the well-being of the animals. Examples of such climate parameters are: temperature, humidity, relative humidity, degree of contamination or content of a polluting element in the air, draught etc. Furthermore, the wording “fixed climate limits” will be used for those limits of the climate parameters which must be obtained to ensure a desired comfort for the animals and reliability of the experiments.
Traditionally, the fixed climate limits are meet by controlling the climate in that area of a building in which the cages are arranged. The climate is, in other words, controlled for a relatively large volume of space, namely an entire building or at least a section of a building in which the cage or cages constitutes only a fraction of the volume. Typically, the climate of the building in question is controlled in a relatively simple manner by use of regular climate control equipment of the kind which can change the temperature in a room of a building, e.g. a regular air-conditioning system. A disadvantage of the traditional way of controlling climate parameters is that an externally generated disturbance can influence the controlled climate, e.g. if a door is opened, or if external weather conditions change rapidly or become extreme whereby the climate control unit may become unable to control the climate within the desired limits.
It may further be a disadvantage if the entire number of cages must have the same climate parameters because they are in one and the same room or building. Sometimes different experiments or different animals may benefit from different climate parameters, and by the traditional method of controlling the climate, this may require the construction of additional buildings, or at least separation of a building space into smaller separate sub-spaces which are separately controllable. Such constructional reorganization of a building is time consuming, and for an extraordinary experiment which may only be carried out in a short period of time, it may imply an irrational cost.
To improve the abilities to carry out experiments on animals in a more flexible manner, and to facilitate good preconditions for the experiments as well as a suitable environment for the animals, cage systems have been developed which comprise a plurality of cages, a surrounding space outside the cages, a plurality of separate internal cage spaces enclosed in the cages, and a climate control unit which is adapted to provide a climate in the cage spaces which is different from that of the surrounding space. Such a system is e.g. disclosed in WO 2007/149528. By control of the climate locally in the cage spaces, the volume of air in the controlled climate can be reduced which may improve the ability to obtain a desired climate in the cage spaces and potentially save energy, because the space in which the climate is to be controlled is limited to where that climate is actually needed, such as where the animals live.
A climate parameter which is often desirable to control in a cage system for experimental animals is the humidity. In many regions around the world, the surrounding air humidity is relatively high, and the main issue in relation to humidity regulation is to lower the humidity in the cages. However, in other regions the humidity varies significantly around the year, and in order to be able to perform controlled experiments, it is therefore desirable to be able to add moisture, typically in the form of steam, to the air in the cages in order to keep the humidity constant. Often used humidifiers are based on piezo-transducers or ultrasound transducers. However, such a humidifier has the disadvantage that the working principle is to generate and eject water droplets into a space of air from where the evaporation takes place; therefore relatively large space is needed. This has not been a problem for air-conditioning systems where the environment is controlled for a whole room or building, but it is disadvantageous for cage systems as described above where it is necessary to control much smaller air volumes, so that the necessary amount of space is not available. Furthermore, systems based on these principle take up relative large space and are therefore typically placed above the ceiling in a room. This is not normally a problem, as traditional air-conditioning systems are part of the permanent installation in a building. However, they are thus not very flexible if a specific laboratory set-up is to be used for a shorter period only. In that case the building-up and removal of a whole system including the air-conditioning may constitute an undesired high proportion of the total cost.
Another possibility would be to use a humidifier based on addition of steam generated under pressure so that precise opening and closing of a valve can be used to add steam. However, such systems require strict safety conditions to ensure safe working environments and are difficult to regulate at very low steam levels. They are also not very flexible with respect to mutual rearrangement of the units of which the systems are made up.